Security threats in SPAs and how to defend against them

Single-page applications (SPAs) offer fast navigation, rich interactivity, and efficient API communication, but this shift to the client has made security responsibilities more dangerous. SPAs hold tokens in browser storage, decide which UI elements to show based on locally stored roles, and manage route access with JavaScript, making security decisions vulnerable to attackers who can inspect, modify, or replay requests with little effort. Common threats include Cross-Site Scripting (XSS), token storage and theft, Broken Object-Level Authorization (BOLA), insecure routing and fake protection, and session and token expiry problems. To defend against these threats, developers should implement practical defenses such as sanitizing user input, storing tokens securely in HttpOnly cookies, enforcing object-level access control, protecting data access on the server, using schema validation libraries, rotating refresh tokens, and keeping third-party dependencies up to date. Additionally, outsourcing security concerns to a hosted login flow with proper cookie-based sessions can significantly reduce exposure to many of these risks.

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